While the filter drier represents a small fraction of the cost of an air conditioning or refrigeration system, its importance should not be trivialized. The filter drier provides assurance to the equipment owner. A properly sized and designed filter drier removes harmful impurities, namely moisture, acid, and solid particles before they can react with system components and shorten the life of the unit. While many products today have the words “filter drier” on them, it does not automatically mean that the system is being protected.
Moisture is by far the most destructive contaminant, regardless of what type of refrigerant is used in the system. By itself, it can cause TXVs to freeze up. But when it reacts with other material, lubricant, and refrigerant in the system, it causes other contaminants such as copper plating, rust, acid, and oil sludge. In order to combat moisture, the desiccant of the drier contains molecular sieve, a porous material that allows water molecules pass through the pores and be adsorbed. If moisture is present, it can lead to the formation of acids that react with system materials, causing component failures and loss of cooling. In order to address the problem of acid, desiccants can also be comprised of some percentage of activated alumina, which helps in the adsorption of acid. As far as solid particle contaminant is concerned, filter driers also contain a filtering media designed to catch and trap these particles, thus preventing them from circulating throughout the system. As refrigerant flows through the filter-drier, harmful contaminants are removed (see exhibit for contaminant removal methods).
If you were to go to any basic HVACR class, the general guideline as to when a new filter drier should be installed is as follows:
• New installation
• Every time a system is opened up and serviced
• After a compressor burnout
• Any time solid or soluble contaminants are suspected in the system.
While it seems like many filter driers are installed over the life of a system, the cost of doing so pales in comparison to replacing a compressor.
Industry Trend
One concerning trend that appears to have entered our industry is the use of low-cost, poorly performing filter driers. Purchasing decisions have been made strictly on price without much regard to the impact that a poor performing filter drier has on the rest of the system. While some of these driers may contain a block of desiccant, they have very little moisture and acid removal capability, along with substandard filtration.
There is an influx of driers with little filtration and no acid removal. As R-22 is phased out and the retrofit refrigerants are used in systems with POE and HFC’s, it is absolutely imperative that the system have a filter drier capable of thoroughly removing contaminants that could wreak havoc on your compressor. Just because you have any, old filter drier on your system, you are not necessarily providing proper protection. Not all filter driers are created equal.
As mentioned earlier, the filter drier is relatively inexpensive when you consider the overall cost of the system. Contractors and service technicians need to keep in mind that when trying to save a few dollars by going with a lower cost filter drier, they might be doing it to the detriment of the compressor.
One of the biggest concerns for contractors is the callback. Callbacks incur costs that the contractor cannot recoup from the end user resulting in lost profits. Even if the component, specifically the compressor, is covered under warranty the contractor is often unable to bill the end user for labor. Quite simply, an inferior filter drier is a risk that is not worth taking.
Chris Urban is currently the system protector product planner for the Emerson Flow Controls business. He has 8 years of industry experience, having held positions in procurement, e-business, and product management.